Mobile communications has changed the way people communicate and mobile phones have been transformed from a luxury item to an essential part of every day life. The use of mobile devices is today dictated by social situations, rather than hampered by location or technology. While voice connections fulfill the basic need to communicate, and mobile voice connections continue to filter even further into the fabric of every day life, the mobile Internet is the next step in the mobile communication revolution. The mobile Internet and/or mobile video are poised to become a common source of everyday information, and easy, versatile mobile access to this data will be taken for granted.
Third generation (3G) cellular networks, for example, have been specifically designed to fulfill these future demands of the mobile devices. As these services grow in popularity and usage, factors such as cost efficient optimization of network capacity and quality of service (QoS) will become even more essential to cellular operators than it is today. These factors may be achieved with careful network planning and operation, improvements in transmission methods, and advances in receiver techniques. To this end, carriers need technologies that will allow them to increase downlink throughput and, in turn, offer advanced QoS capabilities and speeds that rival those delivered by cable modem and/or DSL service providers. In this regard, networks based on wideband CDMA (WCDMA) technology may make the delivery of data to end users a more feasible option for today's wireless carriers. The GPRS and EDGE technologies may be utilized for enhancing the data throughput of present second generation (2G) systems such as GSM. Moreover, HSDPA technology is an Internet protocol (IP) based service, oriented for data communications, which adapts WCDMA to support data transfer rates on the order of 10 megabits per second (Mbits/s).
In addition to cellular technologies, technologies such as those developed under the IEEE 802.11 and 802.16 standards, and/or the digital video broadcasting (DVB) standard, may also be utilized to fulfill these future demands of the mobile devices. For example, wireless local area networks (WLAN), wireless metropolitan area networks (WMAN), and DVB networks may be adapted to support mobile Internet an/or mobile video applications, for example. The digital video broadcasting (DVB) standard, for example, is a set of international open standards for digital television maintained by the DVB Project, an industry consortium, and published by a Joint Technical Committee (JTC) of European Telecommunications Standards Institute (ETSI), European Committee for Electrotechnical Standardization (CENELEC) and European Broadcasting Union (EBU). The DVB systems may distribute data by satellite (DVB-S), by cable (DVB-C), by terrestrial television (DVB-T), and by terrestrial television for handhelds (DVB-H). The standards may define the physical layer and data link layer of the communication system. In this regard, the modulation schemes used may differ in accordance to technical and/or physical constraints. For example, DVB-S may utilize QPSK, DVB-C may utilize QAM, and DVB-T and DVB-H may utilize OFDM in the very high frequency (VHF)/ultra high frequency (UHF) spectrum.
These networks may be based on frequency division multiplexing (FDM). The use of FDM systems may result in higher transmission rates by enabling the simultaneous transmission of multiple signals over a single wireline or wireless transmission path. Each of these signals may comprise a carrier frequency modulated by the information to be transmitted. In this regard, the information transmitted in each signal may comprise video, audio, and/or data, for example. The orthogonal FDM (OFDM) spread spectrum technique may be utilized to distribute information over many carriers that are spaced apart at specified frequencies. The OFDM technique may also be referred to as multi-carrier or discrete multi-tone modulation. The spacing between carriers prevents the demodulators in a radio receiver from seeing frequencies other than their own. This technique may result in spectral efficiency and lower multi-path distortion, for example.
In both cellular and OFDM-based networks, the effects of multipath and signal interference may degrade the transmission rate and/or quality of the communication link. In this regard, multiple transmit and/or receive antennas may be utilized to mitigate the effects of multipath and/or signal interference on signal reception and may result in an improved overall system performance. These multi-antenna configurations may also be referred to as smart antenna techniques. It is anticipated that smart antenna techniques may be increasingly utilized both in connection with the deployment of base station infrastructure and mobile subscriber units in cellular systems to address the increasing capacity demands being placed on those systems. These demands arise, in part, from a shift underway from current voice-based services to next-generation wireless multimedia services that provide voice, video, and data communication.
The utilization of multiple transmit and/or receive antennas is designed to introduce a diversity gain and to suppress interference generated within the signal reception process. Such diversity gains improve system performance by increasing received signal-to-noise ratio, by providing more robustness against signal interference, and/or by permitting greater frequency reuse for higher capacity. In communication systems that incorporate multi-antenna receivers, a set of M receive antennas may be utilized to null the effect of (M−1) interferers, for example. Accordingly, N signals may be simultaneously transmitted in the same bandwidth using N transmit antennas, with the transmitted signal then being separated into N respective signals by way of a set of N antennas deployed at the receiver. Systems that utilize multiple transmit and receive antennas may be referred to as multiple-input multiple-output (MIMO) systems. One attractive aspect of multi-antenna systems, in particular MIMO systems, is the significant increase in system capacity that may be achieved by utilizing these transmission configurations. For a fixed overall transmitted power, the capacity offered by a MIMO configuration may scale with the increased signal-to-noise ratio (SNR). For example, in the case of fading multipath channels, a MIMO configuration may increase system capacity by nearly M additional bits/cycle for each 3-dB increase in SNR.
However, the widespread deployment of multi-antenna systems in wireless communications, particularly in wireless handset devices, has been limited by the increased cost that results from increased size, complexity, and power consumption. Providing separate RF chain for each transmit and receive antenna is a direct factor that increases the cost of multi-antenna systems. Each RF chain generally comprises a low noise amplifier (LNA), a filter, a downconverter, and an analog-to-digital converter (A/D). In certain existing single-antenna wireless receivers, the single required RF chain may account for over 30% of the receiver's total cost. It is therefore apparent that as the number of transmit and receive antennas increases, the system complexity, power consumption, and overall cost may increase. This poses problems for mobile system designs and applications.
Further limitations and disadvantages of conventional and traditional approaches will become apparent to one of skill in the art, through comparison of such systems with some aspects of the present invention as set forth in the remainder of the present application with reference to the drawings.